Voltage regulation.



m. m. N

J L WOODBRIDGE VOLTAGE REGULATION.

APPLICATION FILED DEC. 4, 1914. 1,21 1,803. Patented Jan. 9,1917.

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AIUIIIIIHIMIIIIIIHIP Wl TNESSE S s J. L. WOODBRIDGE.

VOLTAGE REGULATION.

APPLICATION FILED No.4. 1914.

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Patented Jan. 9', 1917.

19m/ocres.

JOSEPH LESTER WOODBBIDGE. OF PHILADELPHIA, PENNSYLVANIA.

VOLTAGE REGULATION.

Specication of Letters Patent.

Patented Jan. 9, 1917.

Application led December 4, 1914. Serial No. 875,420.

To all 'whom 'it may concern:

Be it known that I, JOSEPH LESTER Woon- BRIDGE, a citizen of the United States, and a resident of the city county of Philadelphia, State of Pennsylvania, have invented certain new and useful Improvements in Voltage Regulation, of which the following is a specification.

The principal object of the present invention is to improve voltage regulation by making it more efficient, lreliable, positive and accurate.

In order to accomplish these results, or some of them, 4I employ as part of the controlling circuit a resistor having a temperature co-efficient so markedly negative that over a certain range of current values the voltage across the resistor decreases to a marked extent with increase of current. I combine one or more resistors of this type with other resistance units and with a dynamo field coil of resistance especially designed to combine with the other resistances to give the desired results as more fully explained below.

Stated in general terms the invention comprises a new combination of elements constructed., arranged and combined for co-action in producing a new or improved result.

The invention will be claimed at the end hereof, but will be first described in' connection with the embodiments of it, selected from other embodiments, for the sake of illustration in the accompanying drawings, in which Figure 1 shows diagrammatically a dynamo of the Rosenberg type with field controlling circuits involving features of my invention. Fig. 2 shows diagrammatically a modification of the invention including a Wheatstone bridge for controlling the dynamo field. Fig. 3 is a diagrammaticrepresentation of current and voltage relations in the circuits shown in Fig. 1. Fig. 4 is a modification of the diagram shown in Fig. 3 showing slightly different resistance characteristics, Fig. 5 is a Asimilar diagrammatic representation of the current and voltage relations in the circuits shown in Fig. 2.

Referring to Fig. 1, A is a dynamo of the Rosenberg type fully described in Patent No. 954,468, issued to H. and E. Rosenberg, April 12th, 1910. It consists of a field frame 3 having internally projecting poles 4 between which the armature 5 revolves.

of Philadelphia, in the' The armature is of the bi-polar t pe provided with the usual commutator an four brushes 6, 7, 8 and 9. As shown on this drawing the poles are provided with heavy pole shoes and narrow necks joining the pole shoes t0 the frame. On the neck of each pole is a series winding 10,- and a. shunt winding 11. The general characteristics of this machine are well known, but may be repeated briefiy as follows: When the necks of the poles are excited by current in the windings a small field is produced across the armature which develops a small electromotive force between the brushes 8 and 9. These brushes are short circuited and the iow of current through this short circuit and in the armature winding produces by armature reaction a secondary eld excitation through the armature and heavy pole shoes, as shown by the arrows and this field flux produces the desired voltage @across the main brushes 6 and 7. These brushes are connected to the work circuit 1, 2 through the series winding 10. A storage battery E and translating devices L are shown connected to the wor circuit.

Across the circuit 1, 2 is connected a control circuit containing specially designed resistances 12 and 13. The shunt field winding 11 of the dynamo A is connected between junction point 14 intermediate of the two resistances 12 and 13 and the short circuit connection between the brushes 8 and 9, that is, as here shown to the brush 8. The potential of this brush 8, which is substantially the same as brush 9, is always midway between conductors 1 and 2. Variations in the potential of the point 14 will, therefore, vary the current in the field winding 11. In order to accomplish the desired field control I select for resistance 13 a resistance unit having a very marked negative temperature coefficient such that within certain limits an increase of current in this resistance unit will cause so great a reduction in its resistance that the voltage across its terminals will actually decrease. Such resistance units may be produced by special compositions of boron and carbon, as described in Patents Nos. 1,019,569 to E. Weintraub and 1,094,733 to F. W. Lyle. Resistance 12 may be constant, having a zero temperature coefficient. The characteristics of these two resistances and of the resistance of field winding 11 to produce the results of my invention are shown in the diagram Fig. 3. In this dagram ordinates represent voltages, as Lshown on the vertical scale and abscissae represent current values as shown on thev horizontal scale. The horizontal reference line OX represents the zero of potential corresponding to the potential of-conductor 2 in Fig. 1.

Curve B represents the current and voltage.

' line P which is 18 volts above the line OX will represent the potential of the point8 which is one terminal of the lfield winding 11. If conditions are such that the field winding is carrying no current, its other terminal 14 must be at the same potential namely 18 volts. To bring about this condition resistance 13 must be carrying the current corresponding with this potential of -18 volts, that is, it must be carrying .6 ampere, as indicated by the intersection between the horizontal line P and the curve B. Since the eld 11 is carrying no current under these conditions, the reslstance 12 must be carrying the same current as resistance 13. Resistance 12 must, therefore, be designed to have a drop of 18 volts when carrying .6 ampere. The characteristic line representing resistance 12 is, therefore, the line R in Fig. 3 passing through junction point Q and also through the point corresponding to 36 volts on the vertical axis OY. The voltage drop in resistor 12 as represented byline R is measured downward on OY from poit' 36. The same is true with regard to Figs.

4 and 5. l

It will be seen that resistor 12 must have a rising voltage characteristic, that is, the voltage across its terminals must increase with increase of current and its resistance must be such that .when connected in series with resistor 13 across the circuit 1, 2 and the potential of the junction point 14 11n-L der certain conditions of operation. 'In order that this line D may represent the potential of this junction oint, it is necessary that resistance 13 shall e carryin current represented by the abscissa ST, T eing the point Where the line D crosses curve B. It is also necessary that resistance 12 shall be carrying current represented by the abscissa SU, U being the point where the line D crosses the line R. From thisit is seen that under these conditions resistance 12 must be carrying approximately .43 ampere, while resistance 13 must be carrying approx1 mately .21 ampere. The difference between these two o r .22 ampere is the current which must be transmitted from junction point 14 through iield Winding 11. The potential of the junction point 14 under these conditions is 23 volts, as represented by the ordinate of line D, while the potential of theother end sary to produce the results above described;

.that is, if the vertical distance from the line P to any point T on the line TQ represents thepotential across the field' winding 11' then the horizontal distance TU will represent the current in the field winding. v

If the curve B should coincide exactlywith the straight line TQ between the points T and Q then the regulation for constant voltage would be exact; for the current in the eld could assume any value between zero and that represented by the line TU without any change in the terminal voltage of the machine. If the voltage of the machine should increase slightly and no change in the resistances were to take place there would be a slight increase of current in all branches of the control circuit, but this increase of current in the .c resistance unit 13 would reduce its voltage as shown on characteristic curve B, reducing the potential of the point 14, and, therefore, reducing the flow of current in field winding 11. This reduction would continue until the normal voltage of the machine had been restored. The converse result would follow from a small rise of voltage.

If the curve B deviates slightly from a straight line, as shown in Fig. 3, the voltage will be held approximately constant, but

will vary slightly depending upon the departure of curve B from a straight line.

It is possible, especially in a machine of the Rosenberg type, that the speed may be suiiciently high to generate the desired voltage with the residual magnetism of the ield circuit alone without additional excitation. Under these conditions the current in the field winding will drop to zero represented by the point Q on Fig. 3. If the speed con tinues to increase the current in the field winding will be actually reversed.

Inorder to compensate more exactly for curvature in the line B, resistance 12 may be selected with a slight negative temperature coeiiicient. Its characteristic curve vwill then be represented by the line R in Fig. 4, in which figure the other lines are the same as shown in Fig. 3. If the curvature of the line R is such that the intercepts, such as TU on the abscissa between curves B and R are proportional to the vertical distance between the line P and the line D, for various assumed positions of line D then the current in the field winding, which is represented by the intercepts TU' may assume any value between zero and TU without' any change in the terminal voltage of the machine.

In Fig. 2 is shown a Wheatstone bridge W for controlling the excitation of the field winding 11. The dynamo A1 may be of the same type as that shown at A in Fig.- 1, or may be of any other well known type. The Wheatstone bridge consists of two iixed resistances 15, 16 in opposite branches, while in each of the other two opposite branches are connected two resistance units 17, 17, and 18, 18, having pronounced negative temperature coefficients similar to 18 in Fig. 1. When two such units are connected in parallel only one of them will at any time be operating on that part of the characteristic curve which is over the knee Ordinarily some slight difference between the two would cause one to reach its maximum voltage ahead of the other, and any further increase of current flow through the two in parallel would reduce the voltage across both, the one which had reached-its maximum voltage would pass over the knee of the curve while the other would recede along the initial line. Even if it were possible to conceive of the two operating in parallel at some instant with both units working on the drooping branch of the curve a condition of unstable equilibrium would exist, and any slight change would send an increase of current through one and a decrease through the other which would destroy the equilibrium, and the one whose current had slightly increased would continue to take additional current from the other until the latter had dropped back to the initial branch of the curve when stability would be restored. l

The Wheatstone bridge IV is connected at two opposite junction points to the circuit 1, 2, while the field winding 11 is connected across the other two junction points. Since the two parallel circuits of the Wheatstone bridge connected across the circuit 1, 2 are alike, except that they are inverted with respect to the circuit 1, 2, the potential between conductor 1 and junction point 19, which is one terminal of the field winding 11, will always be the same as the potential between the other junction point 20 and conductor 2f The middle point 21 of the field Winding will, therefore, always be maintained at a potential midway between conductors 1 and 2. It is convenient, therefore,

to represent relations of current and voltage by a diagram similar to Figs. 3 and 4, re re- -field winding. Curve B represents the relation between .current and voltage in one of the resistance units 17. We may assume that this unit is working on the second or drooping branch of its characteristic curve. Inasmuch as the other unit is connected in parallel with this and will be working on the initial portion of the curve, the characteristic curve of the two combined will be represented by a line B1 obtained by adding the current in the drooping branch of B and the current in the initial branch at the same voltage. For example, any abscissa ST of the curve B1 is obtained by adding Sy and Sm. The rest of the diagram is plotted in the same manner as described in connection with Fig. 3 using the curve B1 instead of the curve B as the characteristic of the combined resistances 17, 17.

One advantage of the combination shown in Fig. 2 is that in case one of the resistance units 17 should be accidentally open circuited the other would continue to operate and the results would be nearly the same as those obtained with the two in parallel. The only change would be that instead of working on the curve B1 in Fig. 5 the curve B would represent the new conditions. A slight reduction of voltage across the circuit 1, 2 would result in order that the intercept yU should be equal to the current-which the field could transmit at a potential difference equal to the distance between the line P and the line U.

It will be understood that in Fig. 5 the deviation between the line TQ and the line R, that is, the ratio between the intercept TU and the vertical distance between the line D and the line P now represents the resistance of one-half of the field winding instead of the entire resistance of the field winding, as inthe case of the diagram Fig. 3. It will be further understood that resistances having a slightly negative temperature coefiicient may be used for resistances 15 and 16 as described in connection with Fig. 4.

Having described my invention what I clai and desire to secure by Letters Patent i 1. In combination a dynamo whose voltage is to be maintained at a. desired value, a control circuit connected across the dynamo vterminals including two resistors 1n series whereof the first has a negative temperature coeiiicient. of sufficient magnitude to produce a drooping voltage characteristic with increments of current within certain limiting current Values,l and whereof the second has a rising voltage characteristic and is adapted at the desired dynamo two junction points substantially equal to the difference between the current values necessary in the two resistors to maintain said potential at their junction.

2. In combination, a dynamo whose voltage is to be maintained at a desired value, a Wheatstone bridge connected at two opposite junction points across the dynamo terminals, said bridge having in each of- -two opposite branches two resistors Vin parallel, each having a negative temperature coelicient of suiiicient magnitude to produce a drooping voltage characteristic with increments of current within certain limiting current values, and said bridge having in each of the other two opposite branches a resistor having a rising voltage characteristic and adapted at the desired dynamoA voltage to permit a iow' of current within the range of said limiting current values, and a circuit-containing a coil for controlling the dynamo eld excitation connected across the other two opposite junction points ofthe bridge, said coil circuit being of a resistance suitable at the desired dynamo voltage and with any equal and opposite potential differences within certain limits between each of 'the last named junction points and the mid-potential-between the dynamo terminals to permit av flow of current between said junction points substantially equal to the difference between `the current values necessary in the two resistors on either side of either of said junction points to maintain said potential at their junction.

3. In combination,' a work circuit whose voltage is to be maintained at a desired value, a dynamo connected to said work circuit, a control circuit connected across the work circuit including two resistors in series whereof the irst has a negative temperature oo-eflicient of suiiicient magnitude to produce a .drooping voltage characteristic with increments of current within certain limiting current values and whereof the second has a rising Voltage characteristic and is adapted at the desired voltage on the work circuit to permit a iiow of current through the control circuit within the range of said limiting current values, means forestablishing a junction point intermediate `in lpotential between the conductors of the work circuit and a circuit containing a coil forl controlling the dynamo eld excitation connected between the last named junction point and the junction between the two resistors, said coil circuit having a resistance suitable at the desired work circuitl voltage and with any potential within certain limits at the junction between said resistors .to permit a iiowl of current between said two junction points rov substantially equal to the difference be -tween the current values necessary in the two resistors to maintain said potential at their junction.

4. In combination a work circuit whose voltage is to be maintained at a desired value, a dynamo connected to said work circuit, a Wheatstone bridge connected at two opposite junction points across the work circuit, said bridge having ineach of two opposite branches a resistor having a negative ,temperature co-eficient of sufficient magnitude to produce a. drooping voltage characteristic with increments of current within certain limiting current values, and said bridge having in each of the other two opposite branches a resistor having a rising voltage characteristic and adapted at the desired voltage on the work circuit to permit a flow of current within the range of said limiting current values, and a -circuit containing a coil for controlling the dynamo field excitation, connected across the other two opposite junction points of the bridge, said coil circuit having a resistance suitable, at the desired voltage on the work circuit and with any equal and opposite potential differences within certain limits between the last named junction points and the midpotential of the work circuit to permit a flow of current between said junction points substantially equal to the difference between the current values necessary in the two resistors on either side of either of said junction points to maintain said potential at their junction. s

5. In a constant voltage system the combination of a circuit whose voltage is to be controlled, a dynamo connected 'to said circuit and adapted to controlits voltage, re-

sistors in series relation across said circuit and of which one has a drooping voltage characteristic and the other has a rising voltage characteristic and is adapted to cooperate with the Iirst mentioned resistor over its range of drooping characteristic, means for establishing a junction point of *intermediate potential with respect to the circuit, and a eld regulating coil for the dynamo connected to the junction and to a point intermediate of said resistors, substantially as described.

6. In a constant voltage system the cornbination of a circuit whose voltage is to be controlled7 a dynamo connected to said circuit and adapted to control its voltage, resistors in series relation across said circuit and of which one has a rising and the other a drooping characteristic, means for establishing a junction point of intermediate potential with respect to the circuit, and a ield-regulating-coil circuit for the dynamo connected to said junction and to a point intermediate of said resistors and having a resistance adapted in cooperation with the resistance characteristics of the resistors to permit current in the coil circuit to vary without substantial change in the voltage across the circuit, substantially as described.

7. In a constant voltage system the combination of a circuit whose voltage is to be controlled, a dynamo connected to said circuit and adapted to control its voltage, two resistor elements in series relation across said circuit and of which one has a rising voltage characteristic and the other comprises two resistors in parallel relation each aving a drooping voltage characteristic, means for establishing a junction point of intermediate potential with re ect to the circuit, and a field-regulating-coi circuit for the dynamo connected to said junction, and to a point intermediate of said resistor elements and having a resistance adapted in cooperation with the resistance characteristics of the resistors to permit current in the coil circuit to vary without substantial change in the voltage across the circuit, substantially as described.

8. In a constant voltage system the combination of a circuit whose voltage is to be controlled, a dynamovconnected to said circuit and adapted to control its voltage, two resistor elements in series relation across said circuit and of which one comprises two resistors in parallel relation each having a drooping voltage characteristic and the other has a rising voltage characteristic and is adapted to coperate with the first mentioned resistor element over its range of drooping characteristic, means for establishing a junction point of intermediate potential with respect to the circuit, and a field regulating coil for the dynamo connected to the junction and to a point intermediate of said resistors, substantially as described.

9. In a constant voltage system the combination of a circuit whose voltage is to be controlled, a dynamo connected to said circuit and adapted to control its voltage, resistors in series relation across said circuit and of which one has a drooping voltage characteristic and the other has a rising Voltage characteristic and is adapted to cooperate with the first mentioned resistor over its range of drooping characteristic, means for establishing a junction point of intermediate otential with r ect to the circuit, and a Iield-regulatingcoi circuit for the dynamo connected to said junction point and to a point intermediate of said resistors and having a resistance adapted in coperation with the resistance characteristic of the resistors to permit current in the coil circuit to vary without substantial changel in the voltage across the circuit, substantially as described.

In testimony whereof, I have hereunto signed my name.

JOSEPH LESTER WOODBRIDGE. Witnesses:

JOSEPH H. TRACY, F. G. BEETEM. 

